Used Lionel Legacy SD70-MS with a speaker hum

If you are comfortable removing the cab I would inspect for pinched speaker wire.  Next try swapping RS power supply board with different SD of same vintage.  Next swap the RS board with another loco same vintage.  Last I would use a chip puller and remove and clean edge contacts from the chips and reinstall.

Something else on your loco I noticed at when video stops/ends is that the rear motor looks crooked.  Might want to check that out too while in there.

Thank you Steims.

So doing more looking today I found the problem with the tilted rear motor - there is about 1/8” of free play in the rear truck, like some spacer or similar is missing. Looking at the full side profile, you can see that the rear of the locomotive sits slightly lower than the front. See the attached pic and vid.

The problem with the erratic movement was that the Odyssey control was off. Once I turned that on it, the unit moved out normally.
So there’s the rear truck/tilting motor issue PLUS the loud annoying hum.
Given those problems I think I’m going to return it because it looks like the repairs are above my skill level (and/or too costly to invest if I take it to my hobby shop) on top of the purchase price  

Any additional advice before I do?

Steve, the rear motor mount has some issue.  Maybe a screw is missing and the other loose to behave this way.

Here is the  motor mount (Part 40) which is still available through Lionel parts.

Here is the motor plate that is still available (Part 41).

The truck ears connects to the plate by a 90 degree turn and twist.  Counterclockwise to remove and clockwise to attach.

I would remove the truck and see what part/screw is loose.

Another problem I see is with your locomotive cab on your shell.  It's not on there quite right either.

This loco has been through some things.

Thank you Steims. I had not even noticed the cab misalignment. Definitely some problems and way more than it should have including a broken handrail  

I’m sending it back tomorrow. The seller has been very cooperative so far so I’m grateful for that.

I have about 25 different variations of Lionel's SD70Ace from the early 2006-ish releases to brand new units. I have a few that hum as well which is super annoying. I haven't found a fix for it BUT just know it's common from what I've found.

@Brennenr05 posted:

I have about 25 different variations of Lionel's SD70Ace from the early 2006-ish releases to brand new units. I have a few that hum as well which is super annoying. I haven't found a fix for it BUT just know it's common from what I've found.

Thank you. This was my 3rd SD70 but the only one that had that very loud hum. I sent it back and bought another SD70ACe.

FWIW, my Vision Line Genset has a hum when idle.  Not as loud as your example, but it's there.  This seemed to be an issue with some  of the early Legacy models.  Since all the electronic parts for these models were removed by Lionel and declared as Obsolete, sending it back was the right move, fixing it could have been problematic!

I agree!

This engine is listed on ebay again for parts/repair for $230 with free shipping.

Isn’t that interesting.
I always take pics immediately after unpacking and when I discovered the issues I sent him a message with the pics right then. I even offered to send him the videos but he only said ‘it wasn’t shipped like that’.
So then I told him I was going to return the unit and he did not reply. So I initiated the return for a refund with eBay.
But that wasn’t the end of it. He initially only refunded 50% of the purchase price saying that ‘the locomotive was not like that when he shipped it’(?!).
So I appealed to eBay and they agreed with me and refunded the full purchase price plus tax and shipping.
l’m sure it can be fixed. But at what price?